Generating steering feel for steer-by-wire systems

Abstract

The present invention includes a system and a method for generating steering reaction torque in a steer-by-wire steering system. The system includes a manually steerable member; a feedback generator; a vehicle speed sensor; a steering position sensor; and a steering actuator load sensor. A control unit calculates a set of blended reaction torque values by receiving input signals from the steering position sensor and the steering actuator load sensor. The control unit operates on the input signals and computing a set of reaction torque values, and blending the reaction torque values into set of blended reaction torque values. The set of reaction torque equations comprises a plurality of non-linear functions that is adapted for real-time, continuous operation upon the input signals from the sensors. The set of blended reaction torque values is speed-sensitized based on vehicle speed and transmitted to the feedback generator to generate steering feel in the manually steerable member.

We claim:  
     
       1. A system for generating steerable member reaction torque in a motor vehicle having a steer-by-wire steering system, said system comprising: 
       a manually steerable member;  
       a feedback generator coupled to said manually steerable member for generating a reaction torque;  
       a vehicle speed sensor detecting vehicle speed;  
       a steering position sensor detecting a position of said manually steerable member;  
       a steering actuator load sensor detecting steering actuator load;  
       a control unit calculating a set of blended reaction torque values by (i) receiving input signals from the steering position sensor and the steering actuator load sensor, (ii) operating on said input signals with a set of reaction torque equations for arithmetically computing a set of reaction torque values, and (iii) blending said reaction torque values into set of blended reaction torque values based upon an input signal from said vehicle speed sensor;  
       wherein said set of reaction torque equations comprises a plurality of non-linear functions derived from empirical data and said set of reaction torque equations is adapted for real-time, continuous operation upon the input signals from the vehicle speed sensor, the steering position sensor, and the steering actuator load sensor; and  
       whereby said set of blended reaction torque values is transmitted to said feedback generator such that said feedback generator generates the reaction torque in said manually steerable member.  
     
     
       2. The system of  claim 1  wherein manually steerable member is a steering wheel. 
     
     
       3. The system of  claim 2  wherein steering position sensor is a steering wheel angle sensor. 
     
     
       4. The system of  claim 1  wherein said set of blended reaction torque values is speed-sensitized based upon said speed sensor input signal thereby forming a speed-sensitive reaction torque. 
     
     
       5. The system of  claim 1  further comprising a lateral acceleration sensor. 
     
     
       6. The system of  claim 1  further comprising a yaw rate sensor. 
     
     
       7. The system of  claim 1  further comprising a wheel slip angle sensor. 
     
     
       8. The system of  claim 1  further comprising a lateral acceleration sensor and a yaw rate sensor. 
     
     
       9. The system of  claim 1  further comprising a lateral acceleration sensor and a wheel slip angle sensor. 
     
     
       10. The system of  claim 1  further comprising a lateral acceleration sensor, a yaw rate sensor, and a wheel slip angle sensor. 
     
     
       11. The system of  claim 1  further comprising a yaw rate sensor and a wheel slip angle sensor. 
     
     
       12. A motor vehicle having a steer-by-wire steering system, said motor vehicle comprising: 
       a steering wheel;  
       at least two steerable wheels coupled to a steering actuator for steering the motor vehicle, said steerable wheels mechanically decoupled from said steering wheel;  
       a feedback generator coupled to said steering wheel for generating a reaction torque;  
       a vehicle speed sensor detecting vehicle speed;  
       a steering angle sensor detecting the position of said steering wheel;  
       a steering actuator load sensor detecting steering actuator load;  
       a yaw rate sensor detecting yaw rate;  
       a lateral acceleration sensor detecting lateral acceleration;  
       a wheel slip angle sensor detecting the wheel slip angle of said at least two steerable wheels;  
       a control unit calculating a set of blended reaction torque values by i) receiving input signals from the steering position sensor, the steering actuator load sensor, the yaw rate sensor, the lateral acceleration sensor, and the wheel slip angle sensor, (ii) operating on said input signals with a set of reaction torque equations for arithmetically computing said set of reaction torque values, and (iii) blending said set of reaction torque values into a blended reaction torque value based upon an input signal from the vehicle speed sensor;  
       wherein said set of reaction torque equations comprises a plurality of non-linear functions derived from empirical data and said set of reaction torque equations is adapted for real-time, continuous operation upon the input signals from the vehicle speed sensor, the steering position sensor, the steering actuator load sensor, the yaw rate sensor, the lateral acceleration sensor, and the wheel slip angle sensor;  
       wherein said set of blended reaction torque values is speed-sensitized based upon said speed sensor input signal thereby forming a speed-sensitive reaction torque; and  
       whereby said speed-sensitive reaction torque is transmitted to said feedback generator such that said feedback generator generates said reaction torque in said steering wheel.  
     
     
       13. The motor vehicle of  claim 8  wherein as said speed sensor input signal indicates an increasing vehicle speed, said speed-sensitive reaction torque value is increased such that said reaction torque in said steering wheel is increased. 
     
     
       14. The motor vehicle of  claim 8  wherein as said speed sensor input signal indicates a decreasing vehicle speed, said speed-sensitive reaction torque value is decreased such that said reaction torque in said steering wheel is decreased. 
     
     
       15. The motor vehicle of  claim 8  wherein said steering actuator includes a unitary steering actuator mechanically coupled to said at least two steerable wheels. 
     
     
       16. The motor vehicle of  claim 8  wherein said steering actuator is mechanically coupled to one of said at least two steerable wheels, and further comprising a second steering actuator mechanically coupled to another of said at least two steerable wheels. 
     
     
       17. A method of generating reaction torque in a steer-by-wire vehicle having a manually steerable member, said method comprising: 
       coupling a feedback generator to a manually steerable member;  
       determining vehicle speed;  
       determining a steering position of said manually steerable member;  
       determining a steering actuator load;  
       deriving a set of reaction torque equations;  
       calculating a set of reaction torque values in real-time based upon a determined vehicle speed, a determined steering position, and a determined steering actuator load;  
       blending said set of reaction torque values into a blended reaction torque value based upon said determined vehicle speed;  
       generating said reaction torque in said steering wheel based upon said blended reaction torque value.  
     
     
       18. The method of  claim 17  wherein the step of determining steering actuator load includes sensing steering actuator load, and further wherein the step of determining a steering position of said manually steerable member includes sensing a position of said manually steerable member. 
     
     
       19. The method of  claim 17  further comprising the step of determining a vehicle yaw rate. 
     
     
       20. The method of  claim 19  wherein the step of determining a vehicle yaw rate includes sensing a vehicle yaw rate. 
     
     
       21. The method of  claim 17  further comprising the step of determining a vehicle lateral acceleration. 
     
     
       22. The method of  claim 21  wherein the step of determining a vehicle lateral acceleration includes sensing a vehicle lateral acceleration. 
     
     
       23. The method of  claim 17  further comprising the step of determining a wheel slip angle. 
     
     
       24. The method of  claim 23  wherein the step of determining a wheel slip angle includes sensing a wheel slip angle. 
     
     
       25. The method of  claim 17  further comprising the step of speed-sensitizing said blended reaction torque based upon said determined vehicle speed. 
     
     
       26. The method of  claim 17  further comprising the step of selecting tuning parameters to create a desired steering feel.